"电车用电动机" can be translated as "motor for trolleybus (or tram, depending on the specific type of electric vehicle)" in English.
Here, "trolleybus" typically refers to a bus that draws power from overhead wires, while "tram" generally refers to a passenger vehicle that runs on tracks in the street, often also powered electrically. The choice between "trolleybus" and "tram" may depend on the specific context or the type of electric vehicle being referred to. If the context is clear or if the term is intended to be more general, simply using "motor for electric vehicle" could also be acceptable, though it lacks the specificity of "trolleybus" or "tram."
For a more precise and technical translation, especially in engineering or manufacturing contexts, "motor for trolleybus/tram" would be appropriate.